Studies concerning perinatal heme catabolism and bilirubin production, conjugation and reabsorption are in progress. We are especially interested in elucidating the importance of intrahepatic recirculation of bilirubin in newborn rats and the role of intestinal bacteria in bilirubin reabsorption. Studies are aimed at development of a simple, rapid, in vitro radioassay of the uptake of bilirubin from serum by tissues. Uptake of labeled serum bilirubin by red cells will be correlated with uptake by other tissues (e.g. brain, muscle, liver) in congenitally hyperbilirubinemic rats, and from cord bloods of infants with hemolytic hyperbilirubinemia. The effect of conditions such as hypoglycemia, metabolic acidosis, free fatty acidemia, hemolysis and bile salts on uptake of bilirubin by red cells and other tissues will also be investigated. The effects of phototherapy on liver structure and function will be investigated in newborn normal and jaundiced animals. These studies will compare the relative influence of monochromatic and broad-spectrum light of various intensities on hepatic ultrastructure, liver enzymes, and serum bilirubin, in order to discover safe and effective conditions for phototherapy. Studies are aimed at elucidating the structure of the growth-promoting serum tripeptide described by us. Following structural analysis, we plan to synthesize radioactive tripeptide, in order to examine its interaction with surfaces of various mammalian cell lines, and its assocation with albumin and other serum proteins.